:- module day17.
:- interface.
:- import_module basics.

:- pred run(part::in, lines::in, answer::out) is cc_multi.

:- implementation.
:- import_module char.
:- import_module int.
:- import_module string.
:- import_module list.
:- import_module array.

:- type wind ---> l; r.
:- type cell ---> empty; full.

:- type row   == list(cell).
:- type board == list(row).

:- pred empty(row::in) is semidet.
empty(Row) :- all [X] member(X, Row) => X = empty.

:- func empty = row.
empty = replicate(7, empty).

:- func trim_top0(board) = board.
trim_top0([]) = [].
trim_top0([R | Rs]) = Out :-
  if empty(R) then Out = trim_top0(Rs)
  else Out = [R | Rs].

:- func trim_top(board) = board.
trim_top(B) = [empty, empty, empty | trim_top0(B)].


:- type piece == list(row).

:- func make_piece(list(string)) = piece.
make_piece(Strs) = Piece :-
  if map(row, Strs, Rows) then Piece = Rows
  else die("piece: invalid input").

:- func pieces = array(piece).
pieces = array(['🬋🬋', '🬫🬃', '🬭▌', '▌', '🬹']).

'🬋🬋' = make_piece(["..####."]).
'🬫🬃' = make_piece(["...#...", "..###..", "...#..."]).
'🬭▌' = make_piece(["....#..", "....#..", "..###.."]).
'▌'  = make_piece(["..#....", "..#....", "..#....", "..#...."]).
'🬹'  = make_piece(["..##...", "..##..."]).

:- func piece(int) = piece.
piece(I) = pieces^elem(I `mod` 5).


:- pred left_row(row::in, row::out) is semidet.
left_row([], []).
left_row([empty | Rest], Rest ++ [empty]).

:- pred left_piece(piece::in, piece::out) is semidet.
left_piece(P, Q) :- map(left_row, P, Q).

:- pred right_row(row::in, row::out) is semidet.
right_row(P, Q) :-
  if P = [] then Q = []
  else remove_suffix(P, [empty], P0), Q = [empty | P0].

:- pred right_piece(piece::in, piece::out) is semidet.
right_piece(P, Q) :- map(right_row, P, Q).

:- func row_to_string(row) = string.
row_to_string(Row) =
  from_char_list(map(func(X) = ite(unify(X, empty), '·', '█'), Row)).

:- func piece_to_lines(piece) = lines.
piece_to_lines(P) = map(row_to_string, P).


:- pred cell(char::in, cell::out) is semidet.
cell('.', empty).
cell('#', full).

:- pred row(string::in, row::out) is semidet.
row(Str, Out) :-
  length(Str) = 7,
  map(cell, to_char_list(Str), Out).

:- pred parse(lines::in, array(wind)::out) is det.
parse(Lines, array(List)) :-
  List = map(func(C) = ite(unify(C, '<'), l, r),
             condense(map(to_char_list, Lines))).


run(_, _, Out) :-
  Out = lines(condense(map(piece_to_lines, map(piece, [1,3,1,2])))).